The present invention relates generally to an inflation device and more specifically to a dual stage inflator capable of providing various levels of inflation gas. The invention is specifically designed to achieve a low inflation onset to not injure an occupant, especially a child or a small adult.
Inflatable restraints or airbags have been shown to reduce the seriousness of occupant injury during an automobile crash. An airbag, filled with inflation gas, provides a cushion between a vehicle occupant and the instrument panel or steering wheel. The likelihood of injury is minimized by the airbag absorbing some or all of the kinetic energy associated with the occupant during a crash.
An inflator provides the inflation gas utilized to inflate an airbag. Inflators generally provide inflation gas by burning a pyrotechnic material, releasing stored gas, or by some combination thereof. During a crash, the inflator is actuated to rapidly inflate an airbag. The aggressive airbag deployment has the advantage of getting the inflated airbag in front of the vehicle occupant as soon as possible. The problem associated with aggressive airbag deployment is the possibility of a child, a small adult, or an out of position adult interacting with the airbag while it is being inflated. Out of position is a phrase utilized in the safety restraint industry that refers to an occupant that is not sifting properly in his/her seat or sitting too close to the airbag module.
Dual stage inflators have been developed to reduce the injury to small adults or children by reducing the aggressiveness of airbag deployment. These inflators provide varying output levels of inflation gas in accordance with the size and position of the occupant. The dual stage inflators are able to provide a full output of inflation gas to protect a full size occupant who is not out of position. The dual stage inflator is also able to provide a staged output of inflation gas for the occupants who are smaller is size or out of position. The staged output deployment operates by providing a portion of inflation gas to partially inflate the airbag and after a period of time, the inflator provides more inflation gas to fill the airbag.
Inflators with varying output levels of inflation gas or dual stage inflators have been shown in the past. The dual stage inflators shown in U.S. Pat. No. 6,189,922 B1 and U.S. Pat. No. 6,168,200 B1 have a first and second gas generant. Another variation of the dual stage inflator has two separate burst disks which is illustrated in U.S. Pat. No. 5,022,674, U.S. Pat. No. 5,351,988, and U.S. Pat. No. 5,016,914.
In accordance with the present invention, a low onset dual stage hybrid inflator is disclosed for use in a vehicle. The dual stage inflator comprises a diffuser subassembly, a gas generator subassembly, and a pressure vessel. The diffuser subassembly has a burst disk and an opening device and upon actuation of the opening device, the opening device produces an output energy, which ruptures the burst disk and allows stored gas to escape the dual stage inflator through a flow control discharge opening in the burst disk.
The gas generator subassembly comprises an igniter and a gas generant surrounded by a gas generant subassembly housing. Upon actuation of the igniter, the gas generant is ignited which produces heat and gas that exits the gas generant subassembly housing through a plurality of apertures and enters the pressure vessel containing the stored gas.
The present invention has various output levels associated therewith. For instance, the dual stage inflator can release only the stored gas. The inflator has the option for staged deployment whereby the stored gas is released and after a finite amount of time, the gas generant is ignited. Also, the inflator has the means for full output whereby the burst disk is ruptured at the same time the gas generator subassembly is fired. Another deployment scenario is the firing of the gas generator subassembly only.
In one embodiment of the present invention, the diffuser subassembly and the gas generator subassembly are situated on opposite ends of the dual stage inflator. In another embodiment, the diffuser subassembly and the gas generator subassembly are situated on the same end of the dual stage inflator.